Soil Greenhouse Gas Emissions and Nitrogen Use Efficiency in Corn (Zea mays L) as Affected by Nitrogen Management

Field experiments were conducted to examine the effect of rate, timing and history of urea-ammonium nitrate application on soil greenhouse gas (N2O, CO2 and CH4) emissions, and NUE (agronomic efficiency, AE, and recovery efficiency, RE) in corn at Elora, ON, Canada. Gas emissions were quantified at three rates (30, 145 and 218 kg N ha-1), two timings (N injected in mid-row at planting and at around the V8 growth stage), and two histories (short-term: applying the N rate treatments on plots that had received 145 kg N ha-1 in the previous year, and long-term: applying the same N rate to a given plot over the duration of the trial) of N application for two years (2011 and 2012). NUE was examined over four years (2009 to 2012) using the same treatments as for gas emissions as well as two additional N rates (58 and 87 kg N ha-1). \tIn 2011 and 2012, cumulative N2O emissions during the growing season and corn yields increased significantly with increasing N application rates. Cumulative N2O emissions in 2011 were significantly reduced when N was applied at the V8 stage (0.88 kg N2O-N ha-1) compared to at planting (2.12 kg N2O-N ha-1), with no significant impact on corn grain yield (average 9.1 Mg ha-1). Applying N at the V8 growth stage instead of at planting may be an effective N2O emission mitigation measure without affecting corn yield under conditions when soil moisture content is higher after planting than after the V8 growth stage. \tDuring 2009 to 2012, neither the timing nor the history of N application exerted any significant impact on agronomic efficiency (AE), or estimated maximum economic rate of nitrogen (MERN) and the corresponding corn grain yields. Recovery efficiency (RE) of applied N was significantly improved by N applied at the V8 stage compared to at planting in 2011, and by long-term history of N application compared to short-term history in 2012. \tNeither in 2011 nor in 2012 were the cumulative CO2 and CH4 emissions during the growing season influenced by rate, timing, history, or the interaction of rate and timing of N application.